Electrically programmable fuse using anisometric contacts and fabrication method

ABSTRACT

A fabrication method for fabricating an electrically programmable fuse method includes depositing a polysilicon layer on a substrate, patterning an anode contact region, a cathode contact region and a fuse link conductively connecting the cathode contact region with the anode contact region, which is programmable by applying a programming current, depositing a silicide layer on the polysilicon layer, and forming a plurality of anisometric contacts on the silicide layer of the cathode contact region and the anode contact region in a predetermined configuration, respectively.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a divisional application of application Ser. No. 12/493,616,filed Jun. 29, 2009, now U.S. Pat. No. 8,519,507, the disclosure ofwhich is incorporated by reference herein in its entirety.

BACKGROUND

This invention relates to electrically programmable fuses, and moreparticularly to an electrically programmable fuse including anisometriccontacts and a fabrication method thereof.

Electrically programmable fuses have been employed in many advancedtechnologies within the semiconductor industry. These fuses are utilizedfor various integrated circuit applications such as an implementation ofarray redundancy, field programmable arrays, and in chip-ID, and analogtrimming circuits. These fuses may be programmed to store data on anintegrated circuit, to adjust components on the circuit or to programlogic on the circuit, for example. In a typical electricallyprogrammable fuse the contacts are symmetrically positioned for easierprinting and optimization of contact processing. The term symmetricrefers to the number of contacts and the shape of the contacts beingprimarily squares (i.e., symmetric). Conventional fuses also typicallyhave a large landing region for the contacts, several times the actualfuse link width.

There are several problems associated with the contacts in theconventional fuses. For example, during electromigration, when aprogramming current is applied, instead of heat generation beingconfined to the middle of the fuse link, the contacts can also raise intemperature thereby causing degradation of the contact which may causethe fuse to fail to remain in the programmed state. If a large symmetriccontact is used, while solving the contact degradation issue, thethermal mass of the system increases, thereby requiring very largeprogramming current. The large contact landing region of theconventional fuse also contributes thermal mass, requiring highprogramming current and increasing the risk of contact degradation.

SUMMARY

In an exemplary embodiment, a fabrication method for fabricating anelectrically programmable fuse method includes depositing a polysiliconlayer on a substrate, patterning an anode contact region, a cathodecontact region and a fuse link conductively connecting the cathodecontact region with the anode contact region, which is programmable byapplying a programming current, depositing a silicide layer on thepolysilicon layer, and forming a plurality of anisometric contacts onthe silicide layer of the cathode contact region and the anode contactregion in a predetermined configuration, respectively.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter which is regarded as the invention is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other objects, features, andadvantages of the invention are apparent from the following detaileddescription taken in conjunction with the accompanying drawings inwhich:

FIGS. 1A and 1B are top views of conventional electrically programmablefuses.

FIG. 2 is a top view of an electrically programmable fuse having narrowcontact regions that can be implemented within embodiments of thepresent invention.

FIGS. 3A and 3B are top and side views, respectively of an electricallyprogrammable fuse that can be implemented within embodiments of thepresent invention.

FIGS. 4A and 4B are top views of electrically programmable fuses thatcan be implemented within alternative embodiments of the presentinvention.

FIG. 5 is a top view of an electrically programmable fuse that can beimplemented within alternative embodiments of the present invention.

FIG. 6 is a bell shape curve which illustrates a distribution ofprogrammed resistance of a conventional electrically programmable fusevs. an electrically programmable fuse having narrow contact regions andan electrically programmable fuse according to an embodiment of thepresent invention.

FIG. 7A through 10B are top views and side views, respectively,illustrating various operations of a fabrication method of anelectrically programmable fuse that can be implemented withinembodiments of the present invention.

The detailed description explains the preferred embodiments of theinvention, together with advantages and features, by way of example withreference to the drawings.

DETAILED DESCRIPTION

Turning now to the drawings in greater detail, it will be seen thatFIGS. 1A and 1B illustrate conventional electrically programmable fuses20 and 30, respectively. In FIG. 1A, the conventional electricallyprogrammable fuse 20 includes an array of symmetric contacts 25positioned in a 3×3 arrangement, and in FIG. 1B, the conventionalelectrically programmable fuse 30 includes an array of symmetriccontacts 35 positioned in a 2×1 arrangement. As can be seen in FIGS. 1Aand 1B, the contact regions for which the contacts 25 and 35 arerespectively formed are of a large area for contact processing. Oneproblem associated with the conventional electrically programmable fuseis the possible degradation of the contacts during electromigration,when the programming current is applied to the fuse and heat is appliedto the contacts.

To eliminate some of the problems such as contact degradation,associated with conventional electrically programmable fuses in FIGS. 1Aand 1B, an electrically programmable fuse 40 having narrow contactregions is provided in FIG. 2 according to an embodiment of the presentinvention. The electrically programmable fuse 40 includes a fuse link42, an anode contact region 43, and a cathode contact region 44 wherethe fuse link 42 conductively connects the cathode contact region 44with the anode contact region 43, and is programmable by applying aprogramming current. According to an embodiment of the presentinvention, the anode and cathode contact regions 43 and 44 are narrowerthan that shown in FIGS. 1A and 1B. The narrower contact regions 43 and44 reduce the thermal mass of the system, thereby reducing the currentnecessary to program the fuse. Symmetric contacts 45 are formed on eachof the anode and cathode contact regions 43 and 44 in a 1×4 arrangement.The size of the contacts 45 in the current flow direction is equal tothe size of the contacts in the direction perpendicular to the currentflow direction. The present invention is not limited to any particularnumber of contacts or shape of the contacts as discussed below withreference to FIG. 3A through 5. In addition, a metal layer 46 is formedover the contacts 45 and acts as a heat sink for the anode and cathodecontact regions 43 and 44. The metal layer 46 is isolated from the fuselink 42.

In FIG. 3A there is an electrically programmable fuse 100 according to apreferred embodiment of the present invention. The electricallyprogrammable fuse 100 includes an anode contact region 110, a cathodecontact region 118, and a fuse link 116 conductively connecting thecathode contact region 118 with the anode contact region 110. The fuselink 116 is programmable by applying a programming current. Theelectrically programmable fuse 100 includes a plurality of anisometriccontacts 120 positioned on the anode and cathode contact regions 110 and118, respectively. According to the preferred embodiment of the presentinvention, “anisometric” refers to the dimension of the contact in theone direction being unequal to the dimension of the contact 120 in theother direction (e.g., width of the contact 120 is not equal to thelength of the contact 120). A metal layer 125 contacts the anode andcathode contact regions 110 and 118. As further shown in FIG. 3A, Wfrepresents the width of the fuse link 116 and Lc represents the longerdimension of each contact 120 and Wc represents the smaller dimension ofeach contact 120. According to the preferred embodiment of the presentinvention, Wf<Wc<3Wf and 2<Lc/Wc<10. The contact length Lc is largerthan the contact width Wc. The distance between the contacts 120 islarger than the contact width Wc. According to the preferred embodimentof the present invention, Wf equals the nominal gate length in a giventechnology and may range from approximately 22 nm to approximately 350nm. For example, for given technology node, if Wf=45 nm, then Wc rangesfrom approximately 60 nm to 135 nm and Lc ranges from approximately 120nm to 300 nm). As shown in FIG. 3A, according to the preferredembodiment of the present invention, the anisometric contacts 120include a pair of anisometric contacts aligned in a side-by-sidearrangement such as a 1×2 arrangement on the anode and cathode contactregions 110 and 118, respectively. According to an embodiment of thepresent invention, the width of the anode and cathode contact regions110 and 118 is less than a length of each anisometric contact 120 in acurrent flow direction of the electrically programmable fuse 100.According to another embodiment, the contacts 120 may be alignedorthogonal to the anode and cathode contact regions 110 and 118 (asdepicted in FIG. 4B, for example). The present invention is not limitedto any particular arrangement and number of contacts, and may varyaccordingly. Alternative embodiments of the arrangement of theanisometric contacts will be discussed below with reference to FIGS. 4Aand 4B. Since the fuse 100 includes anisometric contacts 120, uponapplying the programming current to the fuse, the anisometric contacts120 are not heated as much as comparably sized symmetric contacts. Asopposed to the case of symmetric contacts, the anisometric contactsplace the bulk of the thermal mass farther away from the fuse link 116resulting in a lower temperature at the contact interface, therebypreventing the disruption of the liner materials in the contacts 120 andthe degradation of the contact regions 110 and 118. Such degradationstypically result in the diffusion of copper into the fuse link 116causing a failure of the fuse 100.

As shown in FIG. 3B, according to an embodiment of the presentinvention, the electrically programmable fuse 100 is formed by forming apolysilicon layer 210 on a substrate, and forming a silicide layer 215on top of the polysilicon layer 210. The anisometric contacts 120 areformed thereon on the silicide layer 215 and the metal layer 125contacts the contact 120. Additional details concerning a fabricationmethod for forming the electrically programmable fuse 100 will bediscussed below with reference to FIG. 7A through 10B.

As mentioned above, the present invention is not limited to theconfiguration shown in FIGS. 3A and 3B, alternative embodiments of theconfiguration will now be described with reference to FIGS. 4A, 4B and5. As shown in FIG. 4A, an electrically programmable fuse 300 includesan anode contact region 305, a cathode contact region 310, multipleanisometric contacts 315 and a fuse link 320. As shown in thisembodiment, the contacts 315 are positioned adjacent to each other in a2×1 arrangement and the anode and cathode contact regions 305 and 310are increased in width in comparison to those shown in FIG. 3A. Thus,according to one embodiment of the present invention, the contacts 315may be in a n×1 arrangement where n is greater than 1. FIG. 4Billustrates an electrically programmable fuse 350 according to yetanother embodiment of the present invention. As shown in FIG. 4B, theelectrically programmable fuse 350 includes an anode contact region 355,a cathode contact region 360, multiple anisometric contacts 365 and afuse link 370. In the current embodiment, the contacts 365 arepositioned in a vertical direction (i.e., orthogonal to the anode andcathode contact regions 355 and 360). The anode and cathode contactregions 355 and 360 are of a same size as those shown in FIG. 3A. FIG. 5illustrates an electrically programmable fuse 400 according to yetanother embodiment of the present invention. As shown in FIG. 4, theelectrically programmable fuse 400 includes an anode contact region 455,a cathode contact region 460, multiple anisometric contacts 465 only onthe cathode contact region 460 and symmetric contacts 456 on the anodecontact region 455, and a fuse link 470. The purpose of forminganisometric contacts 465 only on the cathode contact region 460 is thatthe degradation of contacts during electromigration typically occurs atthe cathode of the fuse. According to one embodiment of the presentinvention, the anisometric contacts 465 are formed orthogonal to thecathode contact region 460. The present invention is not limited to anyparticular number of anisometric contacts and may vary accordingly.

FIG. 6 is a bell shape curve which illustrates a distribution ofprogrammed resistance of a conventional electrically programmable fuse(as indicated by the reference numeral 60) vs. an electricallyprogrammable fuse having narrow contact regions (as indicated byreference numeral 65) and an electrically programmable fuse according toan embodiment of the present invention (as indicated by referencenumeral 70). As shown in FIG. 6, the distribution of the electricallyprogrammable fuse of the present invention produces a higher medianresistance and a tighter distribution which enables better sensingperformance. Typically the conventional electrically programmable fusehaving symmetric contacts results in a median programmed resistance of1×10⁴ ohms (as indicated by reference numeral 60) and having tail fusesin the distribution coming as low as 1×10³ ohms. The electricallyprogrammable fuse having narrow contact regions has a slightly highermedian resistance of greater than 1×10⁵ ohms (as indicated by referencenumeral 65) and having tail fuses in the distribution coming below 1×10⁴ohms. On the other hand, the electrically programmable fuse having theanisometric contacts according to an embodiment of the presentinvention, has a higher median resistance (as indicated by referencenumeral 70), greater than approximately 1×10⁶ ohms and rarely havingtail fuses with resistances below 1×10⁴ ohms thereby enabling thesensing circuit to work with a wide margin of operation.

FIG. 7A through 10B are top views and side views, respectively,illustrating a fabrication method of an electrically programmable fusethat can be implemented within embodiments of the present invention. Thefabrication method for fabricating the electrically programmable fuse100 shown in FIG. 3A, for example, will now be described below.

In FIGS. 7A and 7B, a silicon substrate 200 is provided and a shallowtrench isolation (STI) 205 is formed over the silicon substrate 200. Apolysilicon layer 210 is then deposited over STI 205. Next, in FIGS. 8Aand 8B, the anode contact region 110, the cathode contact region 118 andthe fuse link 116 are formed via a lithographic patterning process.However, the present invention is not limited hereto and any suitableprocess may be used.

In FIGS. 9A and 9B, a silicide layer 215 is then deposited over thepolysilicon layer 210 on the anode contact region 110, the cathodecontact region 118 and the fuse link 116.

Then, as shown in FIGS. 10A and 10B, a plurality of anisometric contacts120 are formed on the silicide layer 215 of the anode contact region 110and the cathode contact region 118 in a predetermined configuration,respectively.

The present invention provides anisometric contacts which enablessufficient contact area without enlarging the fuse. Therefore, thepresent invention provides no increase in the contact pad size, therebypreserving high density, improved reliability and improvedprogrammability. That is, the improved thermal characteristics of theanisometric contacts also have an advantage in that they enable longerprogramming times and higher programming currents; this enables higherpost-programming resistance and thus enables simpler and more robustsensing circuitry

While the preferred embodiment to the invention has been described, itwill be understood that those skilled in the art, both now and in thefuture, may make various improvements and enhancements which fall withinthe scope of the claims which follow. These claims should be construedto maintain the proper protection for the invention first described.

The invention claimed is:
 1. A fabrication method of an electricallyprogrammable fuse, the method comprising: depositing a polysilicon layeron a substrate; patterning an anode contact region, a cathode contactregion and a fuse link conductively connecting the cathode contactregion with the anode contact region, which is programmable by applyinga programming current; depositing a silicide layer on the polysiliconlayer; and forming a plurality of anisometric contacts on the silicidelayer of the cathode contact region and the anode contact region in apredetermined configuration, respectively, wherein a width of the anodeand cathode contact regions is less than a length of each anisometriccontact in a longitudinal direction of the electrically programmablefuse, and wherein the width of the anode and cathode contact regionsrefers to a dimension perpendicular to the longitudinal direction andalso parallel to a plane of the substrate.
 2. The fabrication method ofclaim 1, wherein forming the plurality of anisometric contactscomprises: forming the anisometric contacts in a side-by-sidearrangement.
 3. The fabrication method of claim 1, wherein forming theplurality of anisometric contacts comprises: forming the anisometriccontacts orthogonal to the anode and cathode contact regions.
 4. Thefabrication method of claim 2, wherein the plurality of anisometriccontacts includes a pair of anisometric contacts formed on the anodecontact region and the cathode contact region, respectively.
 5. Thefabrication method of claim 1, wherein forming the plurality ofanisometric contacts comprises: forming the anisometric contacts in an×1 arrangement where n is greater than
 1. 6. The fabrication method ofclaim 1, wherein a width of the fuse link is less than the width of eachanisometric contact, and the width of each anisometric contact is lessthan three times the width of the fuse link.
 7. The fabrication methodof claim 1, wherein the anisometric contacts are dimensioned inaccordance with the following expressions:Wf<Wc<3Wf;and2<Lc/Wc<10; wherein Wf represents a width of the fuse link, Lcrepresents a contact length of the anisometric contacts in thelongitudinal direction of the electrically programmable fuse, and Wcrepresents a contact width of the anisometric contacts.